This project concerns the genes coding for ribosomal RNA in the lower eukaryote Physarum polycephalum. These genes are located on a giant palindromic DNA molecule which is predominantly extrachromosomal in plasmodia. They can be isolated in milligram quantities together with their associated histones and regulatory proteins. We have cloned restriction fragments of the ribosomal genes and intend to sequence important transcriptional regulatory regions and intervening sequences. We shall elucidate the origin and functions of specific single-strand gaps and tightly-bound proteins at the rDNA termini. We shall examine the association of the rDNA palindrome with chromosomal DNA components. Through use of fluorescent-labeled histone we shall determine the nature of nucleosome structural changes which occur during transcription. We shall continue to examine the location and structure of nucleosomes on transcriptional regulatory sequences and on transcribed and non-transcribed rDNA regions.